Electrofilter for gases

ABSTRACT

A perforated electrode for an electrofilter for gases which includes a sandwich-like arrangement of at least one electrically conductive support layer and a thinner spray discharge layer. The spray discharge layer is formed from a material which has a higher resistance to burning due to spray-discharge than the material of the support layer.

United States Patent Futterer et a1.

1541 ELECTROFILTER FOR GASES [72] Inventors: Dodo Fhttener, Schonbuhlring 37, CH 6000 Luzern; Otto Stem-e, bwaldner l-landelshof, CH 6060 Sar- 1m y ss CH 6072 Sachseln, all of Switzerland [22] Filed: Nov. 24, 1969 [21] Appl. No.: 879,196

(30) Foreign Application Priority Data Nov. 25, 1968 Germany ..P 18 842.4

[52] US. Cl. ..55/150, 29/196, 29/198, 29/199, 55/128, 117/99, 204/ [51] Int. Cl. ..B03c 3/41 [58] Field otSearch ..55/150-152, 101, /2, 128; 117/114 A, 99; 29/196, 198,199; 204/15 [56] References Cited UNITED STATES PATENTS 1,077,977 11/1913 Fuller ..29/199 X 1,322,163 11/1919 Conober ..55/152 1,822,682 9/ 1931 Weiger ..29/198 X 2,047,351 7/ 1936 Alexander ..29/198 UX 2,417,967 3/ 1947 Booe ..29/199 X 2,455,804 12/1948 Ransley et 17/99 UX 47,159 5/1949 rim ..29/199 x 2,477,279 7/1949 Anderson, Jr. ..........29/ 198 X 2,505,907 5/1950 Meston ..55/152 2,579,445 12/1951 Warburton ..55/131 2,625,737 1/1953 Spooner ..29/199 UX 2,771,666 1 1/ 1956 Campbell et a1.............29/198 2,887,406 5/1959 Homer ..29/ 198 X 3,071,491 ll1963 Horn et al................29/196 X 3,085,317 4/1963 Stackhouse ..29/ 198 3,116,981 1/1964 Sayre ..29/198X 3,124,428 3/ 1964 Rabinowicz ..29/126 X 1 51 3,690,043 1 Sept. 12, 1972 3,314,771 4/1967 Hoffmann et al ..29/199 X 3,443,914 5/1969 Hayashi ..29/ 199 X 3,526,081 9/1970 Kusters ..55/ 131 X 935,457 9/ 1909 Bridge ..55/ X 1,787,955 "1931 Rosencrans ..55/ X 1,801,515 4/1931 Marshall ..55/154 X 2,585,777 2/1952 Hills ..55/152 X 2,638,555 5/1953 Marks ..204/312 X 2,881,857 4/1959 Cosby et a1. ..55/152 X 2,929,740 3/1960 Logan ..1 17/114 A UX 2,991,197 7/1961 Sandozetal ..117/114A X 3,054,553 9/1962 White 10/5 UX 3,191,077 6/1965 Marks et a1....................310/5 3,218,431 11/1965 Stauffer ..315/231 X 3,278,331 10/1966 Taylor etal ..117/114A X 3,438,754 4/1969 Shepard et a1. ....l17/114 A X FOREIGN PATENTS OR APPLICATIONS 671,144 9/1963 Canada. ..55/152 360,729 10/1922 Germany ..55/150 371,599 3/1923 Germany ..55/152 344,705 11/1921 Gennany ..55/150 883,876 12/1961 Great Britain...............55/151 OTHER PUBLICATIONS German Printed Application (C) No. 1008259, printed May 16, 1957, KL12e5, lnternat. KL.B01d, (1

sht dwg, 2 pp spec) Primary Examiner-Dennis E. Talbert, .1 r. Attorney-Irving M. Weiner ABSTRACT 2Claims,5l)rawingfigures P'ATE'NTEDREP 12 m2 Fig.

Fig.3

Fig.2

Fig. I

Fig.5

ELECTROFILTER FOR GASES The invention relates to a perforated electrode, and to an electrofilter for gases comprising a sieve-like perforated electrode having sharp-edged perforations and a counter electrode arranged at a distance from said perforated electrode.

Such electrofilters are used to remove impurities, especially dust, from gases. The perforated electrode of an electrofilter serves as corona or spray discharge electrode, whereas the counter electrode spaced therefrom serves as separation or deposition electrode to which the electrically charged dust particles migrate, give up their charge, and then deposit in the collecting chamber.

BACKGROUND OF THE INVENTION The known electrofilters comprising a perforated electrode are generally rotationally symmetrical, the perforated electrode and the counter electrode defining cylindrical surfaces which are coaxial to each other and connected to a voltage source.

Electrofilters may be divided into two types according to their mode of operation. The mode of operation in which the perforated electrode is negative compared with the separation of deposition electrode is of particular interest because of its low voltage requirements. Since the necessary operating voltage depends on the radius of curvature of the perforation edges, which generally adjusts itself to half the thickness of the perforated electrode, the latter should have as small a sheet thickness as possible.

However, for mechanical stability reasons, the sheet thickness of sieves can be reduced only to a limited extent.

The problem underlying the invention is to provide a sieve for electrofilters which has a relatively high mechanical stability, and the perforation edges of which have extremely small radii of curvature which do not become larger even on burning away of the perforation edges.

The solution of this problem is to be seen in that the perforated electrode is constructed in a sandwich-like manner from at least one electrically conductive support layer and a thinner layer (corona or spray discharge layer) fixedly connected thereto, and consisting of a metal or other material of higher resistance to burning away by spray discharge than the material of the support layer. The support layer merely serves to mechanically strengthen the assembly, whereas the thinner spray discharge layer determines the radius of curvature of the perforations.

The present invention provides a perforated electrode which has at least one support layer which is fixedly connected to at least one spray discharge layer. Each spray discharge layer is thinner than each of said support layers. Each spray discharge layer is made from a material, such as a metal, having a higher resistance to burning than the material from which the support layer is made.

According to another embodiment of the invention, the perforated electrode consists of a plurality of support layers and spray discharge layers joined together in alternate succession. This correspondingly increases the area of the sharp edges, and thus also the number of charge carriers emitted from the edges.

The support layer preferably consists of a metal, for example, copper, nickel or iron, whereas the spray discharge layer preferably consists of a material more resistant to burning, such as titanium, tantalium, molybdenum, platinum, tungsten, carbon or alloys thereof.

The spray discharge layer preferably has a thickness of less than microns.

The perforated electrodes may be made by applying by galvanoplastic deposition to a support layer at least one thinner layer of material which is more resistant to burning away than the material of the support layer. This ensures that the spray discharge layer has an uniform and controlled thickness.

The support layer may also be made galvanoplastically be deposition onto a matrix provided with insulating islands. For the correct mode of operation, the configuration of the perforation edges is not important, but what is important is the material selection and the thickness ratios of the support layer and spray discharge layer.

The perforations of the electrode may be made at any desired stage of the production method, for example, by punching a sandwich-like sheet.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in detail hereinafter with the aid of the schematic drawings of several examples or embodiments.

In the drawings:

FIG. 1 shows a cross section through a portion of a perforated electrode according to the invention;

FIG. 2 shows a cross section corresponding to FIG. 1 after the elapse of a certain operating time of the perforated electrode;

FIG. 3 shows a cross section through a portion of a perforated electrode according to the invention comprising one foundation or support layer and two spray discharge layers;

FIG. 4 shows a cross section through a portion of a perforated electrode according to the invention which comprises three support layers and four spray discharge layers;

FIG. 5 shows a perforated electrode on a matrix used to make said electrode.

DETAILED DESCRIPTION OF THE INVENTION The electrofilter or corona discharge electrode illustrated in FIG. 1 includes a support layer 1 of metal which is provided over its surface with numerous perforations 2, only one of which is shown in the figure. The support layer 1 may consist of sheet metal. The perforations 2 may be made in a manner known per se, for example, by punching a metal sheet or by galvanoplastic building up of a metal layer over a matrix provided with insulating islands.

A spray discharge layer 3 is applied in a galvanoplastic manner to one side of the support layer 1 and is substantially thinner than the latter and consists of a material of high resistance to burning up. A high burning resistance in this case means:

1. chemical resistance, particularly to oxygen, nitrogen, hydrogen sulphide and nitrogen-oxygen compounds, since the sheet is no doubt highly heated due to ion bombardment; and/or 2. The atoms of the spray discharge layer are not easily expelled from the surface of the material by heavy positive gas ions.

A resistance to burning is also obtained in particular by means of substances which evaporate only at very high temperatures. Examples of materials resistant to burning are titanium, tantalium, molybdenum, platinum, tungsten, carbon, and compounds and alloys thereof.

H6. 2 shows the perforated electrode according to FIG. 1 after a certain operating time. it is seen that the support layer 1, consisting for example of copper or nickel, has already been noticeably removed at the edge regions 4 of the perforations so that the spray discharge layer 3 projects beyond the support layer, and thus determines the radius of curvature of the spray edge. in general, it may be stated that the radius of curvature is substantially equal to half the thickness of the spray discharge layer 3.

FIG. 3 shows in cross section a portion of a per forated electrode in which spray discharge layers 3 are applied to both sides of the support layer 1. This arrangement has two important advantages over that according to FIGS. 1 and 2. For essentially the same dimensions, the area of the spray discharge layer is twice as large. This, therefore, also increases the number of electrons emitted from the edges for charging the dust particles. Furthermore, after a short operating time a burning away of the support layer 1 occurs as shown by the dashed lines in H6. 3. The space exposed by burning away between the spray discharge layers 3 thus becomes almost field-free so that a further burning away of the support layer 1 occurs only to the extent which the edges of the spray discharge layers 3 are removed. Thus, a material of extremely low resistance to burning may be used for the support layer 1, which affords technological and economical advantages.

In an extension of the idea, a plurality of support layers 1 and spray discharge layers 3 may be arranged in alternate succession. FIG. 4 shows a perforated electrode comprising three support layers 1 and four spray discharge layers 3. This further increases the spray discharge output. The thickness of the support layers is preferably so dimensioned that they are able to lend the perforated electrode sufficient rigidity. The thickness of the spray discharge layers 3 substantially determines the radius of curvature of the spray discharge edges so that the spray discharge layers which are as thin as possible are desirable.

FIG. 5 serves to explain the galvanoplasiic method of making perforated electrodes according to the invention. In the production thereof, a matrix 6 is used in whose surface are embedded islands 7 of insulating material which are located corresponding to the positions of the perforations of the perforated electrode. After passivating the surface 8 of the matrix 6, the support layer 1 is deposited galvanoplastically on the matrix. A thin corona discharge layer 3 of a material of high resistance to burning is then deposited on this support layer, also by galvanoplastic deposition, forming a perforated electrode whose cross section is shown in FIG. 5.

It is, of course, possible to use support layers in the f f 's ed sh ts hich are rforated and then p ei e a slu di s charge lay; by galvanoplastic deposition.

Aitcmatively, perforated electrodes according to the invention can be made by joining a thick sheet of the material of the support layer and a thin sheet of the material of the spray discharge layer by rolling, then further rolling to the desired thickness. The perforations may be made after making the finished sheet by punching.

We claim:

1. A sieve-like perforated electrode having sharpedged perforations and a counter electrode arranged at a distance from said perforated electrode, wherein said perforated electrode comprises at least one electrically conductive support layer, at least one spray discharge layer which is fixedly connected to said support layer in a sandwich-like manner, said spray discharge layer being thinner than said support layer, and said spray discharge layer consisting of a material having a higher resistance to burning due to spray discharge than the material of said support layer.

2. A perforated electrode characterized in accordance with claim 1, including a plurality of said support layers and a plurality of said spray discharge layers arranged in alternate succession and connected together. 

1. A sieve-like perforated electrode having sharp-edged perforations and a counter electrode arranged at a distance from said perforated electrode, wherein said perforated electrode comprises at least one electrically conductive support layer, at least one spray discharge layer which is fixedly connected to said support layer in a sandwich-like manner, said spray discharge layer being thinner than said support layer, and said spray discharge layer consisting of a material having a higher resistance to burning due to spray discharge than the material of said support layer.
 2. A perforated electrode characterized in accordance with claim 1, including a plurality of said support layers and a plurality of said spray discharge layers arranged in alternate succession and connected together. 